If you really want yours firing in high gear, watch out for these sneaky saboteurs.

Skipping meals or going on extreme cleanses

Skipping meals or going on extreme cleanses

Missing out on essential nutrients, especially protein, turns your metabolism sluggish, says registered dietitian Joan Salge Blake, a clinical associate professor at Boston University's Sargent College of Health and Rehabilitation Sciences and a spokesperson for the Academy of Nutrition and Dietetics. It's okay for a few days, but after that, your body switches into “starvation mode,” thinking that it needs to store, not burn, fat to keep you alive. That’s why fasting isn’t a smart idea. The same goes for any crazy diets that encourage you to consume nothing but liquids for more than three days. “When you don’t get enough protein, your body breaks down lean muscle mass, which is what slows your metabolism,” says Blake.

Sitting still

Sitting still

Bad news for the corporate set. “Even if you go to the gym for a half hour every day, if you sit at a desk for eight hours, you still have a sedentary lifestyle,” says Blake. To avoid losing metabolism-boosting muscle mass, which happens when you don't move major muscle groups throughout the day, think about downloading a movement tracking app or buying a gadget like a Fitbit or Jawbone, which alerts you when you've been sitting still for most of the day. Sometimes, that's enough to encourage you to spend half of your lunch hour on a walk, not in the break room.